Skullcap

How to recognise it

Habit

Perennial of 15–50 cm, with square, upright or ascending stems and creeping rhizomes.

Leaf

Opposite, oblong to lance-shaped, 2–5 cm, with a scalloped edge and a heart-shaped base; short-stalked.

Flower

Blue-violet, two-lipped flower of 1–2 cm with a long, slightly curved tube and a pale patch on the lower lip; always in pairs in the leaf axils, facing one way; from June to September.

Fruit/Seed

Four nutlets in the calyx. The calyx has a shield-shaped hump on top and closes after flowering.

Stem

Square, as in all members of the mint family, green or tinged purple.

Confusion with

Lesser skullcap is smaller, has pale pink flowers under 1 cm and grows on wet, acid heath. Selfheal has its flowers in a dense spike at the top. Gypsywort, also found by water, has small white flowers in whorls.

Flowering: June–September · Pruning: March

Why grow it?

• A lovely, understated blue flower for the margin of a wildlife pond or a wet ditch.
• Long flowering season from June to September, with nectar for bumblebees and other bees.
• Grows among reeds, yellow iris and purple loosestrife and fills the margin without taking over.
• Its creeping rhizomes help hold a gently sloping bank together.
• A fascinating plant to look at with children: after flowering the calyx closes like a little helmet over the seeds.

Skullcap: where does it grow best?

• In the wild: banks of ditches, ponds and rivers, reedbeds, wet hay meadows, wet woodland and dune slacks.
• Sun to half shade.
• Wet to moist, moderately rich soil; tolerates short periods of flooding.
• In the garden: the margin of a pond, in wet soil or a few centimetres of water, or along a ditch or rain garden.

Goes well with

• Purple loosestrife: Pinkish purple spikes on the same wet bank, also in summer.
• Water forget-me-not: Small pale blue flowers at the water’s edge.
• Yellow iris: A tall yellow accent in spring.
• Water mint: Fragrant, lilac-flowered and also a member of the mint family of the waterside.
• Meadowsweet: Creamy plumes and a sweet scent in July.

Skullcap: when and how to plant it?

1. Buy plants from a nursery for native aquatic and marginal plants. Never dig plants up along ditches or in nature reserves.
2. Plant in April–May or in September, while the soil is still warm enough for the plants to root.
3. Set the plants 30 cm apart, in groups of three, in wet soil at the pond edge or in a pond basket with poor soil.
4. Do not use potting compost or fertiliser in or around the pond: it encourages algae.
5. You can also sow: in autumn in a pot of wet soil left outside, as the seed germinates better after a winter.
6. Keep the soil wet until the plants are well established.

Care

Water

The soil must never dry out. If the water level drops a lot in summer, top up with rainwater.

Feeding

Not needed and undesirable in and around a pond.

Spreading

Spreads steadily by rhizomes. Too much? Dig out a piece in spring.

Competition

Keep vigorous marginals such as common reed and reed sweet-grass at a distance, or it will disappear.

Letting it seed

Leave the stems after flowering so the seeds can ripen.

Tip: Plant skullcap right on the line where water and soil meet, and keep the most vigorous marginals in check: it will then stay lovely for years between purple loosestrife and water mint.

Pruning and mowing

Pruning months: March.

When: In March, before the new shoots appear.

How:

• Leave the dead stems all winter: they protect the rhizomes and shelter insects.
• Cut them back to just above the ground in March.
• Take the cuttings away from the pond so the water does not become richer in nutrients.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

In April or September, dig out a piece of rhizome with shoots and replant it elsewhere.

Seed

Sow in autumn in a pot of wet soil left outside.

Cuttings

Soft stem cuttings taken in May–June root fairly easily in wet soil.

Skullcap: how does it get through the winter?

Hardy to −30 °C.

• It dies back above ground; the rhizomes overwinter in the wet soil.
• Fully hardy, down to about −30 °C.
• The dead stems shelter small insects and spiders.

Diseases and pests

• Drying out: In a dry summer the plants wilt if the margin dries out. Plant low enough and top up with rainwater.
• Crowding out: Common reed, reed sweet-grass and bulrush overrun it. Thin them out regularly.
• Aphids: Sometimes on the shoot tips; ladybirds clear them up.
• Slugs: Sometimes eat young shoots in spring; usually limited in a natural pond with frogs and toads.

Through the year

• March: Cut the dead stems and take them away from the pond.
• April: New shoots. Plant or divide.
• May: Take soft cuttings. Keep an eye on the water level.
• June: Flowering begins.
• July: Full flower; bumblebees on the flowers. Top up in dry weather.
• August: In flower. Top up in dry weather.
• September: Last flowers, seed ripens. Plant or divide.
• October: Sow in a pot left outside.
• December: Rest. Leave the dead stems standing.

Did you know?

• Scutellaria comes from the Latin ‘scutella’, a small dish or shield, after the hump on the calyx; ‘galericulata’ means ‘wearing a little helmet or cap’.
• After flowering the calyx closes over the nutlets. When they are ripe, the upper lip of the calyx falls off and the seeds are released.
• The English name skullcap refers to the same helmet-shaped calyx.